Process for the isomerization of alkyl benzenes



United States Patent ()filice 3,113,979 Patented Dec. 10, 1963 3,113,979 PROQESS FOR THE ISOMEBIZATION F ALKYL BENZENES Ronald S. Bartlett, Thornton, Glenn 0. Michaels, Park Forest, and Owen H. Thomas, Bolton, IlL, assignors, by mesne assignments, to Sinclair Research, Inc, New York, NFL, a corporation of Delaware No Drawing. Filed Apr. 12, 1960, Ser. No. 21,598

9 Claims. (Cl. 260-668) This invention relates to a process for the isomerization alkyl aromatics.

It is known from the literature that isomerizations involving changes in the carbon content of alkyl groups attached to the aromatic ring, as for instance isomerization of ethyl and larger alkyl group aromatics to their corresponding methyl derivatives, usually proceeds slower than positional group isomerization. Since commercial feeds of interest contain a spectrum of alkyl aromatic derivatives, any product recycle process must minimize these reaction rate differences in order to avoid a buildup non-reactive aromatics in the recycle stream.

One procedure for minimizing any diiferential in reaction rates between these two types of alkyl aromatic isomerization involves the use of a two-stage process. In the first-stage alkyl aromatics are hydrogenated to their corresponding naphthene derivatives and then isomerized. This is followed by a second-stage operation involving naphthene dehydrogenation and final isomerization. The advantage claimed by this two-step approach is that the alkyl aromatic isomerization of certain refractory derivatives proceeds at a faster rate through the naphthene homologues. in most processes, unless the reaction is carried out in two stages, formation of, for example, polymethyl aromatics from their corresponding ethyl and isopropyl aromatic isomers leads to dealkylation side reactions.

We have now discovered a process where both types of isomerization, i.e. positional isomerization and isomerizations involving changes in the carbon content of alltyl groups attached to the aromatic ring, can be carried out in a single stage to produce appreciable yields of the desired product. In the single-stage process of the present invention a fiavorable naphthenearornatic steady state can be attained and the naphthenes can, if desired, be recycled continuously in the mother liquor after removal of the desired isomerate by crystallization. Generally, about 0.1 to- 20%, preferably about 1 to 7 percent, by Weight of naphthenes is produced or is present in the reaction product.

According to the present invention a benzene aromatic hydrocarbon in the C to C range having one or more alkyl groups of 1 to 3 carbon atoms in length, preferably C to C attached to the aromatic ring is contacted under isomerization conditions and in the presence of hydrogen with a catalyst consisting essentially of alumina and catalytic amounts of boria and a plan-tinum group metal.

The isomerization reaction conditions of the present invention include a temperature sufiicient to maintan the alkyl aromatc feed in the vapor phase under the pressure employed. Generally this temperature will be from about 550 to 950 F., preferably about 750 to 825 F., while the pressure will be superatmospheric, for instance, ranging from about 50* to 2000 p.s.i.g., preferably about 150 to 600 p.s.i.g. The catalyst can be used as a fixed, moving or fluidized bed or in any other convenient type of handling system. The fixed bed system seems most advantageous at this time and the weight hourly spaced velocity will in most cases be from about 0.25 to O, preferably about 1 to Free molecular hydrogen must be present in our reaction system and the hydrogen to alkyl aromatic molar ratio will usually be from about 1 to 20:1 or more, preferably about 6 to 122i.

Our hydrocarbon conversion catalyst includes catalytically effective amounts of a noble or platinum group metal and boria supported on an alumina 'base. The catalyst generally contains about 0.05 to 2 weight pencent, preferably 0.1 to 1 weight percent, of one or more of the platinum meta-ls of group VIII, that is platinum, palladium, rhodium, ruthenium, osmium or iridium, with the metals having face centered cubes being preferred. The small amount of noble metal may be present in the metallic form or as a sulfide, oxide or other combined form. The metal may interact with other constituents of the catalyst, but if during use the noble metal be present in metallic form then it is preferred that it be so finely divided that it is not detectable by X-ray difiraction means, -i.e. that it exists as crystals of less than about 50 Angstrom units size. Of the noble metals platinum, palladium and rhodium are used most advantageously.

The boria components is surface dispersible on the support, and therefore it is preferably added in direct proportion to the area of the support. For instance, the amount of boria will usually be about 0.5 to 20 weight percent, and prefer-ably about 5 to 15 weight percent, of the catalyst. These amounts are particularly effective on aluminas having surface areas of about 350 to 600 square meters per gram (BET) before use.

The noble metal and boria constituents of the catalyst are deposited on an absorptive alumina base of the activated or calcined type. The base is usually the major component of the catalyst, generally constituting at least about weight percent on the basis of the catalyst, preferably at least about to The catalyst base is an activated or gamma-alumina such as those derived by calcination of amorphous hydrous alumina, alumina monohydrate, alumina trihydnate or their mixtures. The catalyst base precursor most advantageously is a mixture predominating, for instance about 65 to weight percent, in one or more of the alumina trihydr-ates, bayerite I, bayerite II (randomite or nordstrandite) or gibbsite, and about 5 to 35 weight percent of alumina monohy dnate (boehmite), amorphous hydrous alumina or their mixture. The alumina base can contain small amounts of other solid oxides such as silica, magnesia, natural or activated clays (such as kaolinite, montmorillonite, halloysite, etc.), titania, zirconia, etc., or their mixtures. Although the components of the catalyst can vary as stated, a preferred catalyst contains platinum and boria deposited on activated alumina at least about 200 square meters per gram surface area before use.

As previously stated the preferred catalyst base material is an activated or gamma-alumina made by calcining a precursor predominating in alumina trihydrate. An alumina of this type is disclosed in U.S. Patent No. 2,838,444. The alumina base is derived from a precursor alumina hydrate composition containing about 65 to 95 weight percent of one or more of the alumina trihydrate forms gibbsite, bayerite I and bayerite II (randonrite or nordstrandite) as defined by X-ray diffraction analysis. The substantial balance of the hydrate is amorphous hydrous or monohydrate alumina. Trihydrates are present as well defined crystallites; that is, they are crystalline in form when examined by X-ray diffraction means. The crystallite size of the precursor alumina trihydrate is relatively large and usually is in the to 1000 Angstrom unit range. The calcined alumina has a large portion of its pore volume in the pore size range of about 100 to 1000 Angstrom units generally having about 0.1 to about 0.5 and preferably about 0.15 to about 0.3 cc./ g. of pore volume in this range. As described in the patent the calcined catalyst base can be characterized by large surface area ranging from about 350 to about 550 or more square meters/gram when in the virgin state as determined, for example, by the BET adsorption technique. A low area catalyst base prepared by treating the predominantly trihydrate base precursor is described in U.S. Patent No. 2,838,445. This base when in the virgin state has substantially no pores of radius less than about 10 Angstrom units and the surface area of the catalyst base is less than about 350 square meters/ gram and most advantageously is in the range of about 150 to 300 square meters/gram.

The platinum group metal component of the catalyst can be added to the alumina base by known procedures. For instance, the platinum metal component can be deposited on a calcined or activated alumina, but it is preferred to add the platinum metal component to the alumina hydrate precursor. Thus platinum can be added through reaction of a halogen platinum acid, for instance, fluoro-, chloro-, bromoor iodo-platinic acid, and hydrogen sulfide in an aqueous slurry of the alumina hydrate. The hydrogen sulfide can be employed as a gas or an aqueous solution. Alternatively, the platinum component can be provided by mixing an aqueous platinum sulfide sol with the alumina hydrate. .This sol can be made by reaction in an aqueous medium of a halogen platinic acid with hydrogen sulfide. The alumina hydrate containing the platinum metal can be dried and calcined usually at a temperature from about 750 to 1200 F. or more to provide the activated or gamma-alumina modifications. The boria can be added to the catalyst in any stage of its preparation. It may be incorporated in the support, for instance, by precipitation, coprecipitation, impregnation, and mulling either before or after the addition of the group VIII metal. It can also be applied by impregnation from solution (water, organic or inorganic solvents) or from a gas phase. However, it is frequently added to the catalyst after it has been formed by tableting or extrusion and calcined. After the boria is added in this procedure the catalyst can be recalcined. Preferably, the boria is added by pouring a hot solution of boric acid over the platinum alumina catalyst, stirring thoroughly, and then drying and calcining.

The catalyst of the present invention can be easily regenerated employing conventional procedures, for instance, by subjecting it to an oxygen-containing gas at temperatures suiiicient to burn off carbon deposited on the catalyst during the conversion of petroleum hydrocarbon feedstock. This oxy-gen-containing gas, e.g. an oxygenmitrogen mixture, can contain about 0.01 weight percent to 5 weight percent oxygen but preferably contains about 0.5 to 1.5 weight percent oxygen and is introduced at a flow rate such that the maximum temperature at the site of combustion is below about 1000 F.

The alkyl aromatic feed material employed in our process is a material that contains as a major fraction a C to C benzene aromatic hydrocarbon having attached to its aromatic ring one or more alkyl groups in the C to C carbon length range, preferably 1 or 2 carbon atoms. The preferred alkyl aromatic feeds are those containing C C and C derivatives as the major fraction. C derivatives can be obtained from durene crystallized mother liquors which are composed of durene, isodurene, small amounts of prehnitene with the remainder being primarily ethylxylenes.

The following specific examples will serve to illustrate our invention but are not to be considered limiting.

EXAMPLE I 300 grams of a calcined platinum-alumina catalyst of the type described in U.S. Patent No. 2,838,444 were Weighed into a 6" crystallizing dish. The catalyst analyzed 0.6% platinum and at the time of platinum addition and before calcination the alumina comprised about trihydrate (42% bayerite, 18% randomite, 11% gibbsite) with the remaining being substantially of the amorphous or monohydrate forms. After calcination at a maximum temperature of about 925 F. the catalyst composition had an area (BET method) within the range from about 350 to 550 square meters per gram. 59 grams of H BO were dissolved in 279 ml. of deionized water by heating to boiling. The hot boric acid solution was poured over the platinum-alumina catalyst and stirred thoroughly with a rubber spatula. The catalyst was placed in a forced air drying oven, set at 284 F. for 4 hours. The catalyst was stirred occasionally while drying. The ovendried catalyst was transferred to a sagger and placed in a Table I XYLENE ISOMERIZATION Catalyst 0.6% Pt-10% boria alumina Pt-SiOrAl20s Single stage Single stage Two stage Processing conditions Temperature, F.. 800 800 800 800 800 800 850 850 Pressure, p.S.l.g 113g 2153 115i 315% 175 175 175 175 2nd 6.11 1.0 1.0 1.0 Sta e Hz/I'I'C mole ratio 12. 4 10.2 8.5 9. 5 9. 2 10 g Feed composition, wt; percent:

uene 0.5 1.1

4. 2 24. 7 19. 6 0.5 14.6 31.9 0.8 0.8 Y 92. 8 48. 2 46.1 98.1 98.1 p-Xylene 1.5 7.1 11.2 0.7 1.1 1.1 P.O.N. (paraffins, olefins and naphthenes) 1.0 1.4 0.8 E Product distribution, Wt. percent:

Paraflins 7.0 2. 7 4.3 1. 7 3.5 3. 8 3. 9 3.3 Ethylbenzene 5. 4 6. l. 7. 7 10. 8 15. 7 13. 7 0.2 3. 3 0- ylene. 18.2 24. 3 16. 5 17. 3 16. 4 24. 1 23. 9 24. 1 m-X ylene- 38. 6 38. 7 38. 3 41. 3 40. 3 36.8 44. 6 43.8 pXylene. 17. 8 15.8 17.2 17. 0 17.1 14. 4 22. 4 22. 4 Benzene... 0.5 0.5 1.5 0.9 0.9 Tolnene 3. 6 1. 4 5. 9 3. 3 2. 5 2 9 4.2 2.1 Co aromatlcs 5.1 4. 7 5. 3 3.0 1.6 G nanhthenes 3. 5 5. 8 3.3 3. 3 2. 7 4. 3 0 1. 1 Yields: b

o-Xylene: percent olequilibriurn 100 79 92 89 81 83 100 115 mXylene: percent of equilibrium.. 100 95 100 100 106 86 96 103 p-Xylene: percent of equilibrium..- 103 86 104 91 89 76 117 114 Ethylhenzene: percent of equilibrium- 88 68 49 55 2 39 Selectivity to Ca derivatives 84 91 83 9O 92 93 92 95 a Data from LE Qhem, April 1955, p. 770. b Percent of equilibrium yield for a given isomer is defined as times the mole fraction of a given isome r m normalrzedCs rsomeratc e ther divided into or by the equilibrium isomer mole fraction depending on whether feed composition 15 short or in excess of equilibrium.

mufile furnace preheated to 1000 F. The catalyst was held at 1000 F. for 2 hours and cooled in a desiccator. Analysis 9.95% B EXAMPLE II In Table II, for example, the ethylbenzene conversion of the process of the present invention was 64 compared to 62 for the two-stage process while the xylene yields were in general quite similar. The advantages of the present process over the single-stage method represented by the A 1" universal stainless steel reactor is charged w1th bli h d d are apparent 88 100 cc. of a latinum-alumina-boria catal st g p Y EXAMPLE 1v prepared essentially as above. Hydrogen flow is maintained at a rate of 0.5 to 1.0 cubic foot per hour for 3 In accordance with the general procedure of Example hours to insure platinum reduction. At this time alkyl I a tetra-methy-lbenzene feedstock was isomerized using aromatic feeds A, B and C were passed over the catalyst the catalyst of Example I to produce the desirable chemifrom a pump and the reaction was conducted under the cal intermediatedurene. The results are shown in Tables conditions shown in Table I. At the end of a threc- Illa and H11). hour reaction period the runs Were terminated and the Table 111::

1 products analyzed by mass spectrograph infra red. ISOMERIZATION OF TETRAMETHYLBENZENES The results are shown in Table I. In addition, pub- I 0 atalyst. 0.6% Pt-10% Bzoa-Alzos lished data 011 PX'OCGSSES employing a platlnum-SiOg- Feedstock: Durene crystallizer mother liquors. A1 0 catalyst in single and two stages are shown for O comparison. The reaction conditions and feeds employed 288 288 288 in these nuns and the results found are also shown 1n 2O HSV 5 10 Table I Hz/HC mole IZLiLlO 1O 10 10 T "\Yt. percent naphthenes. "ll-1.5 EXAMPLE 1H Liquid product yield 90 94 97 Ethyl benzene was isomerized in accordance with the Feed general procedure of Example I employing the catalyst 5 1 2 of that a p For pa q p p pdbhshed Dummfisodumnmm 0.20 m data showing ethyl benzene 1somer1zed in a single and equilibrium value 0.82 twostage processes using plat1num-S1O Al O catalyst are;1 giveii. ThehreactionTcbolnditlions feed compositions Table 1111,

own in an resu ts are s a e ISOMERIZATION or C10 AROMATICS-MOTHER LIQUORS Table H FROM DURENE CRYSTALLIZER Catalyst: 0.07 Pt-lOV BZOii-AlzO ETHYLBENZENE ISOMERIZATION Conditions: 000 n, 100 p.s.i.., 4 Wfisv, 2 1 Hii n'o mole ratio.

0.6% Pt- PlI-SiOrAlzOs Feed Run 10% Bzoa- Catalyst alumma- Single stage Single stage Two stage u ef ellsodurene ratio 0.13 0.64 Liquid product recovery, wt. percent 99. 4

Processing conditions:

Temperature, "F 800 800 80 EXAMPLE V 175 175 175 2nd E mole ratio $32 8 8 Stage Several isomerization runs were conducted employmg peedcomposmon ffigg as catalysts the platmnm-boriaalumlna of Example I,

galumina impregnated with 10% boria and platinum alu- 1:0--- mina (prepared as in Example I). The feed composipxylene r tions, reaction conditions and results are shown in Table p 40 1V. Product distribution wt. percent:

Parafiins 1 4.0 2.7 3.0 Table IV Ethyllbenzeneg g l1i $Z 1 1 2412 catalyst 0.0 Pc1o% B20:-A120310% p-Xylene. 11. 4 7. 5 12. 2 2Oa-A120a0.6% Pt-AhO; Benzene- 2.5 Toluene 3. 7 3.0 2. 3 Cu ar0matics 2. 9 Single Stage 00 naphthenes 5.8 3.2 4. 8 g i z percent of equimy Processing conditions:

m 50 5e 82 g ggg 2 i ressurc p.s.1.g.. 7. 75 rifiili ff 'jfifffi fffFE??? 59 34 57 2.95 p Xy1ene: percent of equflib Hi/HC more ratio 10.2 10.4 10.2

rium 66 33 53 Feed composition, wt. percen Ethylbenzene: percent of 301216716 equiubrium 9 13 21 .Jthylbemenm 99.7 Selectivity to O3 derivatives, wt. o'xyline 6 percent 87 2% 7.1 7.1 Ethylbenzene conversion 64 RON: n L 4 n 14 4 Prodpct Xdistribution, wt percent. 7 4 3 b are 2. .0 1. 1.6 0.7 Definedmqiablel Ethylbcnzeue. 6.1 ass 0.8 80.4 2.1 A comparison of the data 1n Tables 1 and II shows o-Xgl ncfln 5%. gs 3%. 52,: that both positional group isomerization and those in- H 335 553; :3 volving side chain contraction and expansion can be 60 ene. 0.5 2.5 0.4 5.7 h 1 alu in at Toluene..- 1.4 3.7 0.7 5.8 5.8 carried out in one stage wit. p a mum orla m a cg+ammamsl 29 51 Q4 conversion levels comparable to or better than those gnian n s 5.8 5.8 3.0 1.0 4.4 obtained with platinum on silica-alumina in twohstagesCi fjgg i enttoffequig i m 7g 59 7 0 25 1 a n g 0 an myenezpereen o equii riuru 95 59 84 0 66 In Table I for examp the y f q of p-Xylenc: percent olequilibrium 86 66 50 5 76 para xylenes (percent of equilibrium) in the first run Ethylbemene; percent Oimluilib.

. t e riurn 85 19 11 9 25 (A) Wkiwh employed the smg1 esflge process of th Selectivit; to Cgderivativcs 91 87 9'1 82 87 present invention, were substantially that produced by Xylene 73 52 35 the two-stage process, yet the process of the present inh'lhylbemene conversion 64 19 vention yielded 80% (of equilibrium) of ethylbenzene compared to the 39% yielded by the two-stage process. Defined as 111 Table Examination shows that the absence of platinum on the boria impregnated alumina results in a composition that is significantly inferior both for positional group isomerizations as well as the type involved in Xyleneethyl benzene interconversion. In addition, the data of Table IV indicates the advantageous effect of boria on an 0.6% Pt-A1 O catalyst when used for alkyl aromatic isomerization. Even when operating at a 100 F. higher temperature at a lower space velocity, Xylene isomerization with platinum-alumina gives a lower conversion than that found for its boria-containing analogue.

We claim:

1. A process for the isomerization of C to C alkyl benzene hydrocarbons having at least one alkyl group containing 1 to 3 carbon atoms which comprises contacting a feed consisting essentially of alkyl aromatic hydrocarbons containing at least a major fraction of said C to C alkyl-benzene hydrocarbons under vaporphase isomerization conditions at a temperature of about 550 to 950 F. and in the presence of free hydrogen with a catalyst consisting essentially of alumina and catalytic amounts of boria and a platinum group metal the isomerizate reaction product having about 0.1 to 20% naphthene.

2. The process of claim 1 wherein the alkyl group contains 1 to 2 carbon atoms.

3. The process of claim 2 wherein the catalyst consists essentially of alumina, about 0.1 to 1 weight percent of platinum group metal and about 5 to 15 Weight percent boria.

4. The process of claim 3 wherein the platinum group metal is platinum.

5. The process of claim 4 wherein the alumina is derived by calcination of hydrous alumina containing about to percent trihydrate and has a surface area of about 350 to 550 square meters/ gram before use.

6. The process of claim 1 wherein the temperature is about 750 to 825 F.

7. The process of claim 4 wherein the temperature is about 750 to 825 F.

8. The process of claim 7' wherein the isomerizate product has about 1 to 7% naphthene.

9. The process of claim 1 wherein the isomerizate product has about 1 to 7% naphthene.

References Cited in the file of this patent UNITED STATES PATENTS 2,478,916 Haensel et al Aug. 16, 1949 2,751,333 Heinemann June 19, 1956 OTHER REFERENCES Sachanen: The Chemical Constituents of Petroleum (1945), page 214, published by the Reinhold Publishing Company, New York. 

1. A PROCESS FOR THE ISOMERIZATION OF C8 TO C10 ALKYLBENZENE HYDROCARBONS HAVING AT LEAST ONE ALKYL GROUP CONTAINING 1 TO 3 CARBON ATOMS WHICH COMPRISES CONTACTING A FEED CONSISTING ESSENTIALLY OF ALKYL AROMATIC HYDROCARBONS CONTAINING AT LEAST A MAJOR FRACTION OF SAID C8 TO C10 ALKYL-BENZENE HYDROCARBONS UNDER VAPORPHASE ISOMERIZATION CONDITIONS AT A TEMPERATURE OF ABOUT 550 TO 950*F. AND IN THE PRESENCE OF FREE HYDROGEN WITH A CATALYST CONSISTING ESSENTIALLY OF ALUMINA AND CATALYTIC AMOUNTS OF BORIA AND A PLATINUM GROUP METAL THE ISOMERIZATE REACTION PRODUCT HAVING ABOUT 0.1 TO 20% NAPHTHENE. 